Heating and cooling systems in large office buildings or apartment complexes are generally controlled, in individual rooms, by room temperature sensors and thermostat control devices. Such thermostat control devices generally include a setpoint control device, for setting a desired room temperature, a room temperature sensor, for sensing the actual room temperature, and a communication mechanism for sending the setpoint and temperature information to a controller for determining the difference between the desired and actual room temperature and for sending a control signal to the central heating and cooling system indicating temperature adjustment needs.
From a users perspective, a thermostat control device's main function is setpoint adjustment. Setpoint controls are generally regarded as the main interface between the user and the device. Therefore, readability and ease of use of the setpoint controls are of the utmost importance.
Setpoint controls include a display device (in one or more embodiments), for displaying the current room temperature and setpoint, and a set point adjustment control, for adjusting the setpoint. Traditionally, setpoint adjustment has been accomplished by a controlling device reading either a resistance or a current which corresponds to a particular setpoint temperature.
Potentiometers have been used for setpoint adjustment when the controlling device reads a resistance. However, because the resistance is continuously variable in a potentiometer, repeatability (the specific resistance at a particular point of travel) is usually poor. Also, the temperature coefficient associated with low cost potentiometers is poor adding further inaccuracy.
Circuits containing transistors, resistors and potentiometers have been used for setpoint adjustment when the controlling device reads a current. A variable resistance potentiometer, without any additional circuitry, would result in a nonlinear current change as a function of position. Therefore, additional active circuitry is required to produce a linear current change as a function of position. In addition to the limitations of potentiometers, as described above, the active circuitry produces additional inaccuracies and cost.
Display devices have progressed from mercury-based thermometers and dials to liquid crystal display (LCD) devices. Once again, accuracy and ease of use are essential. The user must be able to easily read and operate the display device in order for it to be effective. Even the most efficient heating/cooling systems will be ineffective if the user has difficulty operating the device properly.
The heating and cooling systems mentioned above generally maintain a database of setpoint and actual temperatures for the individual rooms at controllers. The database values can usually be viewed and manipulated using a central console or maintenance terminal. In this way, a technician or building manager can adjust the setpoints in individual rooms from one central location. In addition, the maintenance terminals can be used to upload software upgrades as well as perform other maintenance functions. The maintenance terminal is generally connected to the controller in some central location which can be difficult to get to.
Accordingly, it is a general object of the present invention to provide an improved thermostat control device adapted for controlling the temperature in a space which is accurate and easy to use.
It is another object of the present invention to provide an improved setpoint control device which is accurate and easy to use.
It is still another object of the present invention to provide an improved thermostat control device which can also be used as a maintenance terminal for viewing and adjusting database points stored at the controller to which the thermostat control device is attached.
It is a further object of the present invention to provide an improved thermostat control device which contains a man-machine interface port for connecting a maintenance terminal to the temperature control system.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings.